A question I’m often asked is: "If the group I’m interviewing with has a casual dress code policy, and I hear they all wear jeans and sneakers, should I still dress up for my interview?"
The answer is yes, you should always dress up (meaning wearing a business suit) for interviews, unless the hiring manager specifically tells you otherwise. (No, I wouldn’t ask him or her if I could come in in casual wear.) While the employees may enjoy the freedom from a business dress code, they almost inevitably expect job candidates to come in dressed nicely and "easy on the eye." In other words, while they wear jeans and sneakers themselves, they usually don’t want to see a candidate in jeans and sneakers. After all, you are not one of them, yet. Plus, dressing up conveys a sense of respect for the interviewers.
On a releated note, I’d also like to caution ladies not to don sexy apparel for a job interview, especially when it comes to skirt and shoes. If you go to an interview dressed in a revealing skirt or sexy high-heeled pumps, you essentially devalue yourself as a future quant. Chances are, the heterosexual male interviewers will probably love to sit in the same room with you, but their opinions of your quant qualifications likely won’t be enhanced by your appearance alone. Besides, even if your sexiness wins you the job, would you really want to work for guys who hired you so they can leer at you day in and day out?